Sharing of information such as files, data, and the like, sharing of peripheral equipment such as a printer, and the like, or exchange of information such as transfer of E-mails, data contents, and the like, can be realized by connecting multiple computers to form a LAN.
Heretofore, LAN connection has been generally made by a cable such as an optical fiber, coaxial cable, or a twist pair cable, but this case needs a line laid-down construction, which prevents a network from simple establishment, and also complicates lead wiring of cables. Also, even following establishment of a LAN, the movement range of equipment is restricted due to a cable length, which is inconvenient.
Wireless LANs have attracted a great deal of attention as a system for liberating users from LAN cables of the wired method. According to a wireless LAN, the most part of cables in the work space such as an office can be omitted, so communication terminals such as personal computers (PC) can be moved with relative ease.
In recent years, the demand thereof has been markedly increased along with speeding up and price-reduction of a wireless LAN system. Particularly, in these days, implementation of a personal area network (PAN) has been studied for establishing a small-scale wireless network between multiple electronic apparatuses present around a personal environment to perform information communication. For example, different wireless communication systems and wireless communication apparatuses have been stipulated by using frequency bands not requiring the authorization of a competent authority, such as THE 2.4-GHz band, 5-GHz band, or the like.
Examples of the standard specifications relating to a wireless network include IEEE (The Institute of Electrical and Electronics Engineers) 802.11 (e.g., see Non-patent Document No. 1), HiperLAN/2 (e.g., see Non-patent Document No. 2 and Non-patent Document No. 3), IEEE802.15.3, and Bluetooth communication. As for the IEEE802.11 standard, various types of wireless communication method such as the IEEE802.11a standard, IEEE802.11b standard, and the like are available according to the differences of wireless communication methods and frequency bands to be used.
In general, in order to form a local area network using wireless technology, a method is employed wherein one apparatus serving as a control station called an “access point” or “coordinator” is provided within the area, and then a network is formed under totalized control of this control station.
With a wireless network in which an access point is disposed, in the event that information transmission is performed from a certain communication apparatus, an access control method based on a band reservation has been widely employed wherein a band necessary for information transmission thereof is reserved for the access point first, and a transmission path is utilized so as not to collide with information transmission in one of the other communication apparatuses. That is to say, wireless communication is performed synchronously such that communication apparatuses within the wireless network are synchronized one another by disposing the access point.
However, with a wireless communication system including an access point, in the event that asynchronous communication is performed between the communication apparatuses of the transmission side and the reception side, wireless communication always needs to be performed via the access point, and consequently, a problem wherein utility efficiency of a transmission path is reduced by half is caused.
On the other hand, “Ad-hoc” communication wherein wireless communication is performed direct-asynchronously between terminals has been devised as another method for forming a wireless network. In particular, with a small-scale wireless network made up of relatively few clients positioned nearby, the AD-hoc communication is appropriate wherein wireless communication of direct synchronization can be performed between arbitrary terminals without utilizing a particular access point.
An Ad-hoc wireless communication system includes no central control station, so is appropriate for forming a home network made up of domestic electric appliances, for example. An Ad-hoc network has characteristics wherein routing is automatically changed even if one terminal fails to operate properly, or becomes power-off, so is hardly collapsed, and accordingly, data can be transmitted relatively away while maintaining a high-speed data rate by hopping a packet multiple times between mobile stations. As for an Ad-hoc system, various development cases have been known (e.g., see Non-patent Document 4).
Incidentally, under a work environment wherein information devices such as a personal computer (PC) and the like have become widely used, and a great number of devices are mixed within an office, it is assumed that communication stations are scattered, and multiple networks are established in overlapped manner. Under such a situation, in the case of a wireless network employing a single channel, there is no room for retrieving the situation even if another system interrupts during communication, or communication quality deteriorates due to interference or the like.
To this end, with a conventional wireless network system, a method has been generally employed wherein multiple frequency channels are prepared for coexistence with another network beforehand, and one frequency channel to be used in a wireless communication apparatus serving as an access point is selected to start operation.
According to such a multi-channel communication method, when another system interrupts during communication, or communication quality is deteriorated due to interference or the like, network operation is maintained, and coexistence with another network can be realized by switching a frequency channel to be used.
For example, with a high-speed wireless PAN system of IEEE802.15.3 as well, multiple frequency channels available for the system are prepared, a wireless communication device confirms existence of a device which is sending a beacon signal as a piconet coordinator (PNC) to the surrounding area following power being turned on, and accordingly, an algorism is employed wherein a frequency channel to be used is selected by performing scan operation as to all available channels.
With an autonomous decentralized Ad-hoc network in which a control station is not disposed, resource management regarding frequency channels is important to suppress interference with a different wireless network which is running in the vicinity as much as possible. However, in order to switch a frequency channel to be used for the system all at once, a representative station called an access point needs to instruct each terminal station regarding a utility channel. In other words, it is difficult to switch a frequency channel with an Ad-hoc network.
In order to switch between multiple frequency channels, upon HiperLAN/2 being taken as an example, a method for switching the channels all at once has been conceived. For example, an AP (base station) serving as a central control station repeatedly informs MTs (mobile stations) connected to the AP that frequency channels are changed, and the AP and MTs switch the utility channels all at once. Determination regarding whether or not switching should be done is made on the initiative of the AP. Information necessary for this determination can be acquired through the following processing procedures, for example.
(1) According to the instructions of the AP, the MTs which are connecting therewith suspend communication temporarily, scan another frequency channel to perform channel quality evaluation, and inform the AP of the result thereof.
(2) According to the instructions of the AP, the AP suspends transmission of an annunciation channel temporarily, and the MTs now connecting to the AP scan the current frequency channel in use, also perform channel quality evaluation, and inform the AP of the result thereof, and the information is collected by following such procedures.
Also, with Bluetooth communication, a method has been employed wherein each frequency channel is fairly utilized by hopping frequencies with a central control station called a master serving as the basis. In order to form a network, the existence of the master serving as the basis of synchronization between the hopping pattern of a frequency channel and the time axial direction is indispensable. In the event of the master disappearing, the network formed so far once becomes a disconnected state, and the processing for selecting a new master becomes necessary.
Also, with a wireless LAN system of the IEEE802.11 series, a network is formed using the frequency channel set by an access point first, and accordingly, it is difficult to establish an Ad-hoc network without disposing a base station. In the event of performing communication with a wireless communication apparatus (terminal) accommodated in an AP which runs with another frequency channel, between the APs needs to be connected with a wired LAN cable, for example. That is to say, unless between the APs which are accommodated is connected, communication cannot be performed even if wireless communication apparatuses (terminals) which physically adjacently exist are accommodated in a different AP.
Also, with a high-speed wireless PAN system of IEEE802.15.3 as well, it is possible to perform scan of all frequency channels first, and search of coordinators existing in the vicinity, but once implementation using a particular frequency channel is started, the utility situations of other frequency channels cannot be comprehended. Accordingly, even if a piconet using a different frequency channel exists in the vicinity, communication with a wireless communication apparatus connected to the piconet cannot be performed.
Thus, with a conventional wireless communication method, a complex mechanism is necessary, such as timing of switching frequency channels, set-up processing realized by message exchange and the like for terminals, which participate in a network, starting frequency channel switching operation in sync with one another, arbitration processing for determining frequency channel switching, and the like. Also, the existence of a central control station is necessary, such as an AP in IEEE802.11 and HiperLAN/2, or a master in Bluetooth communication, which performs control independently. If the central control station such as an AP, master, or the like disappears, some kind of protocol processing or human-induced setting modification work becomes necessary for selecting a new central control station instead of that central control station, which causes a problem wherein communication is disconnected during that processing.
Also, a wireless communication system has been proposed wherein a frequency channel is determined by measuring not only the interference of the local station channel but also interference using an adjacent channel (see Patent Document 1), but this is a system in which multi-channels are realized by intervening of a base station, so cannot be applied to an autonomous decentralized system.
For example, a method can be conceived wherein a traffic receiving channel is specified by a communication station sending a beacon over the channel most appropriate for the local station. However, even if that channel is most appropriate for the local station, that channel may be a channel which provides interference to a communication station receiving the beacon. It is needless to say that the beacon sending channel which a communication station selected on the basis of the local station is not always a channel which all peripheral communication stations can receive.
Also, in the event that the beacon sending channel of one station is the channel which cannot be used in the other station due to a interference channel or deterioration of communication quality, even if these communication stations can communicate with each other over another channel, these communication stations get trapped in a deadlock state in which they cannot acknowledge one another's existence eternally.
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. 6-37762
[Non-patent Document 1]
International Standard ISO/IEC 8802-11: 1999(E) ANSI/IEEE Std 802.11, 1999 Edition, Part11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications
[Non-Patent Document 2]
ETSI Standard ETSI TS 101 761-1 V1.3.1 Broadband Radio Access Networks (BRAN); HIPERLAN Type 2; Data Link Control (DLC) Layer; Part1: Basic Data Transport Functions
[Non-Patent Document 3]
ETSI TS 101 761-2 V1.3.1 Broadband Radio Access Networks (BRAN); HIPERLAN Type 2; Data Link Control (DLC) Layer; Part2: Radio Link Control (RLC) sublayer
[Non-Patent Document 4]
C. K. Tho; Ad Hoc Mobile Wireless Network (Prentice Hall PTR)
It is an object of the present invention to provide an excellent wireless communication system, wireless communication apparatus and wireless communication method, and computer program, which can preferably form a network by between communication stations mutually operating in an autonomous decentralized manner without interference under a communication environment in which multiple channels are prepared.
It is another object of the present invention to provide an excellent wireless communication system, wireless communication apparatus and wireless communication method, and computer program, which can perform channel access using multiple frequency channels effectively in an autonomous decentralized wireless network which requires no particular control station.
It is a further object of the present invention to provide an excellent wireless communication system, wireless communication apparatus and wireless communication method, and computer program, which can avoid a deadlock state in which each of communication stations cannot acknowledge one another's existence to form an autonomous decentralized multi-channel wireless network.
The present invention has been made in light of the above problems, and a first aspect thereof is a wireless communication system for forming an autonomous decentralized network using multiple communication stations having no relationship between a control station and controlled stations under a communication environment in which multiple channels are prepared;
wherein each communication station transmits a beacon signal in a certain cycle using the channel which many more peripheral stations can receive.
Note, however, that the term “system” here means a logical group made up of multiple devices (or function modules for realizing a particular function), and whether or not each device or each function module is accommodated in a single casing is irrelevant.
With an autonomous decentralized wireless network, each of communication stations can acknowledge the network configuration thereof by informing beacon information within a transmission frame cycle, and performing scan operation of a beacon signal from one of the other stations. However, in the event of an autonomous decentralized network utilizing multi-channels, transmission frames are configured so as to be overlapped over the frequency axis for the amount of the number of utility channels, so the communication stations cannot receive a beacon unless they make the transition to over the same channel at the beacon sending timing of another communication, and accordingly, it is hard for a new participating station to determine the beacon sending timing and sending channel of the local station.
Also, even if the communication station is most appropriate for the local station, that channel may be the channel which provides interference to one of the other stations serving as an other communication party. It is needless to say that the beacon sending channel which a communication station selected on the basis of the local station is not always the channel which all peripheral communication stations can receive. For example, in the event that the beacon sending channel of one station is the channel which cannot be used in the other station due to a interference channel or deterioration of communication quality, even if these communication stations can communicate with each other over another channel, these communication stations get trapped in a deadlock state in which they cannot acknowledge one another's existence eternally.
With the present invention, an arrangement is made wherein the communication stations describe the level information of interference which the local station receives in a beacon signal which is periodically transmitted by each communication station (or some kind of signal for informing interference information), and transmit this. Consequently, the communication stations determine a communication channel following comprehending interference situations based on the received beacon information from peripheral stations. Accordingly, with the present invention, the communication channels can be controlled in an autonomous decentralized manner by avoiding that the channel which terribly provides interference to the peripheral stations is utilized as a communication channel.
The communication stations select the channel which many more communication stations can receive as a beacon sending channel based on the interference information of each channel described in a beacon signal when new participation or refresh. Also, in the event that there is a peripheral station which cannot receive a beacon, the beacon sending channel is attempted to be changed.
Thus, according to the present invention, in light of the interference levels of peripheral stations over each channel, an arrangement is made by selecting the channel which many more communication stations can receive as a beacon sending channel, so becoming trapped in a deadlock state in which they cannot acknowledge one another's existence eternally can be avoided as much as possible. Also, each communication station does not need to switch the channel during a period in which there is no sending data, and only reception of a beacon is being performed.
The communication stations can reduce overhead necessary for exchange of (RTS/CTS) packets, and channel transition by utilizing the same communication channel as that of a peripheral communication station as much as possible if the interference which the local station receives is an acceptable level.
Also, the communication stations may perform data sending operation using a channel other than a beacon sending channel. For example, based on the interference information obtained from the beacon signal of an other communication party, a traffic may be transmitted using the most appropriate channel having a low interference level between the communication stations.
The communication stations may determine a beacon sending channel according to regarding whether or not the local station needs a wideband, for example. For example, in the event that the local station needs a wideband, the channel which is preferably not used by other communication stations, and has a low interference level for the local station is selected, and transmission of a beacon is started. The same operation is performed regardless of whether the local station is the transmission side or the reception side.
On the other hand, the communication station which does not need a wideband, upon considering overhead and the like when changing a channel, preferably transmits a beacon over the same channel as a peripheral communication station, so focuses on the channel which the most communication stations transmit a beacon (most frequent channel).
In the event that peripheral stations including the local station do not receive great interference over the most frequent channel, transmission of a beacon is started using this channel. Also, in the event that the multiple communication stations receive so great interference that they cannot receive a beacon transmitted at the lowest rate, the channel which causes the average interference level to the lowest is selected, and transmission of a beacon is started there.
Also, according to a wireless communication system according to the present invention, following transmission of a beacon, comings and goings of traffics can be managed in an autonomous decentralized manner by giving a preferential communication right to the beacon sending station thereof. At this time, following transmission of a beacon, the channel preferentially utilized may be changed to the channel most appropriate for traffic transmission other than the beacon sending channel according to the interference situation on the reception side.
Also, with an autonomous decentralized wireless communication system according to the present invention, random access based on (CSMA/CA) can be performed during a period other than a preferential sending period disposed immediately following a beacon sending timing over each channel. At this time, the (RTS/CTS) method can be employed as means for avoiding a collision and improving communication quality. With this communication method, the communication station serving as a data sending source transmits a request to send packet (RTS) over the beacon sending channel of the communication station serving as a data sending destination, and starts data transmission in response to receiving a clear to send packet (CTS) from the communication station serving as the data sending destination.
Now, the communication station serving as the data sending source may transmit a beacon multiplexed with the (RTS) signal over the beacon sending channel prior to transmission of the (RTS) signal, assuming that a communication station serving as a hidden terminal exists from the perspective of the communication station serving as the data sending destination. A peripheral station which received such a beacon attempts to avoid interference by withholding transmission of data for a predetermined period over a channel wherein data transmission is performed based on the (RTS/CTS) procedures.
At this time, in the event that the beacon sending channel of the data sending source is identical to the beacon sending channel of the data sending destination communication station, the beacon multiplexed with the (RTS) signal is regarded as the (RTS) signal itself. Also, the communication station serving as the data sending destination can start data transmission by feeding back the (CTS) signal in response to receiving the relevant beacon. Thus, the overhead of the (RTS/CTS) procedures at multi-channels can be reduced by omitting retransmission of the (RTS) signal.
Also, a second aspect of the present invention is a wireless communication system for forming an autonomous decentralized network using multiple communication stations having no relationship between a control station and controlled stations under a communication environment in which multiple channels are prepared;
wherein each communication station transmits a beacon in a certain transmission frame cycle over the beacon sending channel of the local station, and also in the event that the beacon sending channel set by the other station which does not need to perform communication is different from the channel which the local station now uses, each communication station omits receiving operation of a beacon from the relevant other station so as not to perform channel switching for reception of a beacon.
As described above, the wireless communication system according to the first aspect of the present invention is a multi-channel-type autonomous decentralized network, so the communication stations can set the most appropriate channel to the beacon sending channel of the local station.
Now, each communication station needs to perform notification regarding comprehension for existences of peripheral stations, and a network state by transmitting a beacon in a certain transmission frame cycle, and also receive a beacon from the peripheral stations. With a multi-channel-type network, in order to transmit a beacon, the communication stations need to make the transition to the beacon sending channel in sync with the beacon sending timing of each peripheral station. However, channel switching requires a period of around 300 μsec or so from the perspective of hardware operation. Consequently, in the event that the communication station which is communicating data suspends data communication to receive a beacon from one of the other stations, performs channel transition and reception of a beacon, following which makes the transition to the original channel to resume data communication, overhead becomes great.
To this end, with the second aspect of the present invention, an arrangement is made wherein in the event that the communication stations comprehend that the beacon sending timing of one of the other stations approaches, the communication stations determine regarding whether or not there is the need to communicate with the relevant beacon sending station, and then in the event that there is no need to receive a beacon, and also the current utility channel is different from the beacon sending channel, beacon receiving operation is omitted.
Thus, omitting unnecessary beacon receiving operation enables time necessary for beacon transition and power consumption of an apparatus to be omitted, and also enables communication capacity to be increased.
Now, with a wireless communication system according to the present invention, comings and goings of traffics is managed in an autonomous decentralized manner by providing a preferential communication right to a beacon sending station (described above), but the beacon sending station does not always acquire a preferential transmission right based on a beacon sending channel. That is to say, the beacon sending station may change a channel which can be used preferentially to the channel most appropriate for traffic transmission other than the beacon sending channel depending on the interference situation on the reception side.
The beacon sending station may make the transition to another channel immediately after sending a beacon to start data communication, but upon the communication station omitting beacon receiving operation, such channel transition operation cannot be acknowledged. To this end, the communication station, in the event of omitting beacon receiving operation, estimates the sending timing regarding the (RTS) and (CTS) signals based on the beacon sending timing, performs receiving operation over the current utility channel only for that timing, and detects regarding whether or not the beacon sending station has made the transition to the current utility channel.
Subsequently, in the event that the communication station detects that the beacon sending channel has made the transition to the current utility channel at the sending timing of the (RTS) and (CTS) signals, the communication station avoids a communication collision by withholding data communication operation of the local station. On the other hand, in the event that the communication station does not detect that situation, the communication station acknowledges that the beacon sending station has acquired a preferential transmission right based on another channel, and continuously performs data communication operation of the local station over the current utility channel.
Thus, in the event of omitting beacon receiving operation of one of the other stations, there is no need to perform unnecessary channel transition, and also a communication collision can be avoided by the beacon sending station performing receiving operation for a certain period during the preferential sending period acquired through beacon transmission.
Also, a third aspect of the present invention is a wireless communication system for forming a network based on Ad-hoc communication using multiple communication stations having no relationship between a control station and controlled stations under a communication environment in which multiple channels are prepared;
wherein each communication station transmits a beacon over the beacon sending channel most appropriate for own reception, and also performs transmission of data using the beacon sending channel of the communication station serving as a data sending destination.
With the third aspect of the present invention, an arrangement is made wherein each communication station selects a channel having communication quality most excellent for the local station as a beacon sending channel, and disposes the beacon sending timing of the local station over this channel to perform beacon transmission. In the event that the beacon sending timing of an existing station has been already set over the own beacon sending channel, the own beacon sending timing is determined so as not to overlap temporally. The information of interference from which each channel suffers for example, and so forth are described on beacon information. Also, the communication stations, according to the beacon sending timing of one of the other stations, make the transition to the beacon sending channel of that station to perform beacon reception.
On the other hand, when the communication stations transmit data, the communication stations perform data transmission using the channel having excellent communication quality appropriate for reception in the communication station serving as a data sending destination, regardless of the beacon sending channel of the local station. Regarding which channel communication quality is appropriate for each communication station can be readily determined by which channel the communication station thereof uses to perform beacon transmission.
Thus, each communication station determines a beacon sending channel only depending on the interference situation of the local station, and this is familiarized to the public as a channel for receiving the traffic of the local station, which facilitates control in each communication station under a multi-channel autonomous decentralized communication environment.
Here, each communication station may acquire a preferential sending period along with the beacon sending timing of the local station.
Also, each communication station makes the transition to the beacon sending channel of one of the other stations along with the beacon sending timing of that station, and receives a beacon, following which is allowed to perform data sending operation over a channel other than that beacon sending channel even during a preferential sending period provided to that station over that beacon sending channel.
For example, a certain communication station performs data transmission using the beacon sending channel of the communication station of a sending destination using a preferential sending period acquired following beacon transmission. Subsequently, during the preferential sending period, upon the beacon receiving timing of one of the other stations approaching, the communication station once suspends transmission, and makes the transition to the beacon sending scheduled channel thereof. With the channel serving as the transition destination, one of the other stations utilizes a preferential sending period, but in the event that the channel serving as the transition destination is different from the channel utilized by the local station, the local station can return to the original channel to continue data sending operation.
Therefore, according to the present invention, each communication station can determine a communication channel in an autonomous decentralized manner, and avoid interference effectively, and also improve communication capacity drastically by utilizing multiple channels effectively.
Also, with an autonomous decentralized wireless communication system according to the present invention, random access based on (CSMA/CA) can be performed during a period other than a preferential sending period disposed immediately following a beacon sending timing over each channel. At this time, the (RTS/CTS) method can be employed as means for avoiding a collision and improving communication quality.
In such a case, the communication station serving as a data sending source transmits the request to send packet (RTS) over the beacon sending channel of the communication station serving as a data sending destination, and starts data transmission in response to receiving the clear to send packet (CTS) from the communication station serving as the data sending destination.
Also, the communication station serving as the data sending source may transmit a beacon in which the communication station serving as the data sending destination and the beacon sending channel thereof are specified over the beacon sending channel of the local station prior to transmission of the (RTS) signal, assuming that a communication station serving as a hidden terminal exists from the perspective of the communication station serving as the data sending destination. A peripheral station which received such a beacon attempts to avoid interference by withholding transmission of data for a predetermined period over the beacon sending channel of the communication station serving as the data sending destination, i.e., a channel wherein data transmission is performed based on the (RTS/CTS) procedures.
At this time, in the event that the beacon sending channel of the data sending source is identical to the beacon sending channel of the communication station serving as the data sending destination, the beacon in which the communication station serving as the data sending destination and the beacon sending channel thereof are specified is regarded as a pseudo-RTS signal. Also, the communication station serving as the data sending destination can start data transmission by feeding back the (CTS) signal in response to receiving the beacon in which the communication station serving as the data sending destination and the beacon sending channel thereof are specified. Thus, overhead of the (RTS/CTS) procedures at multi-channels can be reduced by omitting the transmission procedures of the (RTS) signal (retransmission of the (RTS) signal).
Also, a fourth aspect of the present invention is a computer program which is described in a computer-readable format so as to execute on a computer system the processing for operating in an autonomous decentralized manner under a wireless communication environment in which multiple channels are prepared, having no relationship between a control station and controlled stations, the program comprising:
a channel setting step for setting a data sending/receiving channel;
a communication control step for controlling transmission and reception of data;
a beacon generating step for generating a beacon signal including the level information of interference which the local station receives; and
a beacon analyzing step for analyzing the beacon signal received from a peripheral station;
wherein in the channel setting step, a communication channel is determined based on the interference level information included in the beacon received from a peripheral station following comprehending the interference situation of each channel at the peripheral station.
Also, a fifth aspect of the present invention is a computer program which is described in a computer-readable format so as to execute the processing for operating in an autonomous decentralized manner under a wireless communication environment in which multiple channels are prepared, having no relationship between a control station and controlled stations, the program comprising:
a beacon sending step for setting the beacon sending channel of the local station, and sending a beacon;
a beacon receiving control step for controlling beacon receiving operation from a peripheral station;
a beacon analyzing step for analyzing the beacon signal received from a peripheral station; and
a communication control step for setting a data communication channel, and controlling data communication operation;
wherein the beacon receiving control step including:                a sub step for comprehending that the beacon sending timing of the other station approaches;        a sub step for determining regarding whether or not there is the need to perform communication with the relevant beacon sending station; and        a sub step for omitting beacon receiving operation in the event that there is no need to receive a beacon, and also the channel which the local station now uses is different from the beacon sending channel.        
Also, a sixth aspect of the present invention is a computer program which is described in a computer-readable format so as to execute the processing for operating in an autonomous decentralized manner under a wireless communication environment in which multiple channels are prepared, having no relationship between a control station and controlled stations, the program comprising:
a channel setting step for setting a data sending/receiving channel;
a communication control step for controlling data sending/receiving timing;
a beacon generating step for generating a beacon signal of the local station; and
a beacon analyzing step for analyzing the beacon signal received from a peripheral station;
wherein in the channel setting step, of the multiple channels, the own beacon sending channel is determined, and also the beacon sending channel of the communication station serving as a data sending destination is determined as a data sending channel when transmitting data.
The computer program according to each of the fourth through sixth aspects of the present invention is defined as a computer program which is described in a computer-readable format so as to realize predetermined processing on a computer system. In other words, by installing the computer program according to each of the fourth through sixth aspects of the present invention on a computer system, collaborative operation is exhibited on the computer system, which operates as a wireless communication apparatus. A wireless network is established by activating a plurality of such wireless communication apparatuses, whereby the same advantages as the wireless communication system according to each of the first through third aspects of the present invention can be obtained.
Advantages
The present invention provides an excellent wireless communication system, wireless communication apparatus and wireless communication method, and computer program, which can preferably form a Ad-hoc network without mutual interference between communication stations under a communication environment in which multiple channels are prepared.
Also, the present invention further provides an excellent wireless communication system, wireless communication apparatus and wireless communication method, and computer program, which can perform channel access using multiple frequency channels effectively in an autonomous decentralized wireless network which requires no particular control station (access point, base station, master, etc.).
Also, the present invention further provides an excellent wireless communication system, wireless communication apparatus and wireless communication method, and computer program, which can avoid a deadlock state in which each of communication stations cannot acknowledge one another's existence to form an autonomous decentralized multi-channel wireless network.
A multi-channel autonomous decentralized wireless communication system according to the present invention can preferably avoid a deadlock state between communication stations, and also improve the throughput of the entire system by effective frequency assignment, and further reduce influence to another system.
Also, the multi-channel autonomous decentralized wireless communication system according to the present invention, by transmitting a beacon, needs to perform comprehending the existence of a peripheral station, and notification of a network status, and also receiving a beacon from peripheral stations, but by omitting unnecessary beacon receiving operation, can omit time necessary for beacon transition and power consumption of an apparatus, and can increase communication capacity.
Also, in the event of omitting beacon receiving operation, by estimating the sending timing of the (RTS) and (CTS) signals based on the beacon sending timing, and performing receiving operation over the current utility channel only for that timing, unnecessary channel transition can be omitted, and also a communication collision can be avoided.
Also, the multi-channel autonomous decentralized wireless communication system according to the present invention can improve the throughput of the entire system, and also can reduce influence to another wireless system in the vicinity by each communication station performing frequency assignment effectively, and performing flexible interference avoidance. Also, multiple channels can be used simultaneously, so even in this point, the throughput of the entire system can be improved.
Other objects, characteristics, and advantages regarding the present invention will be apparent with more detailed description based on later-described embodiments of the present invention and the appended drawings.